U.S. patent number 5,952,088 [Application Number 08/995,982] was granted by the patent office on 1999-09-14 for multicomponent fiber.
This patent grant is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Brian T. Etzel, Fu-Jya Tsai.
United States Patent |
5,952,088 |
Tsai , et al. |
September 14, 1999 |
Multicomponent fiber
Abstract
Disclosed is a thermoplastic composition comprising an unreacted
mixture of an aliphatic polyester polymer as a continuous phase,
polyolefin microfibers as a discontinuous phase encased within the
aliphatic polyester polymer continuous phase, and a compatibilizer
for the aliphatic polyester polymer and the polyolefin microfibers.
The multicomponent fiber exhibits substantial biodegradable
properties and good wettability yet is easily processed. The
thermoplastic composition is useful in making nonwoven structures
that may be used in a disposable absorbent product intended for the
absorption of fluids such as body fluids.
Inventors: |
Tsai; Fu-Jya (Appleton, WI),
Etzel; Brian T. (Appleton, WI) |
Assignee: |
Kimberly-Clark Worldwide, Inc.
(Neenah, WI)
|
Family
ID: |
26710368 |
Appl.
No.: |
08/995,982 |
Filed: |
December 22, 1997 |
Current U.S.
Class: |
428/297.7;
428/221; 525/190; 525/166; 428/300.7; 524/378; 525/186; 525/177;
428/299.7; 428/480; 524/513; 428/297.4 |
Current CPC
Class: |
A61L
15/225 (20130101); D01F 6/92 (20130101); C08L
67/02 (20130101); C08L 67/04 (20130101); D01F
6/46 (20130101); C08L 67/02 (20130101); C08L
23/00 (20130101); C08L 67/04 (20130101); C08L
23/00 (20130101); Y10T 428/249921 (20150401); Y10T
428/24995 (20150401); Y10T 428/249947 (20150401); Y10T
428/249941 (20150401); Y10T 428/31786 (20150401); Y10T
428/24994 (20150401) |
Current International
Class: |
C08L
67/04 (20060101); C08L 67/02 (20060101); C08L
67/00 (20060101); A61L 15/22 (20060101); A61L
15/16 (20060101); D01F 6/92 (20060101); D01F
6/46 (20060101); C08L 067/02 (); B32B 027/02 ();
B32B 027/36 () |
Field of
Search: |
;524/378,513
;525/166,177,186,190 ;428/297.4,297.7,299.7,300.7,221,480 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 080 274 A2 |
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Jun 1983 |
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EP |
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0 394 954 A2 |
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Oct 1990 |
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EP |
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0 765 913 A1 |
|
Apr 1997 |
|
EP |
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40 16 348 C2 |
|
Nov 1991 |
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DE |
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5-71005 |
|
Mar 1993 |
|
JP |
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8-260320 |
|
Oct 1996 |
|
JP |
|
WO 92/04410 A1 |
|
Mar 1992 |
|
WO |
|
WO 94/17226 A1 |
|
Aug 1994 |
|
WO |
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WO 95/08660 A1 |
|
Mar 1995 |
|
WO |
|
WO 95/17216 A1 |
|
Jun 1995 |
|
WO |
|
Other References
Derwent World Patent Database abstract of DE 40 16 348 C2:
Description of V. Sturm et al., "Nonwoven Fabric Composite For
Hygiene Articles Etc.". .
Abstract of JP 8-260,320: Description of Hiroshi Nishimura et al.,
"Soft Nonwoven Fabrics of Biodegradable Short Fibers For Disposable
Diapers and Sanitary Napkins." .
Derwent World Patent Database abstract of JP 06-248,551 A:
Description of Kuraray Co. Ltd., "Aliphatic Polyester Based Melt
Blown Nonwoven Fabric." .
Patents Abstracts of Japan JP 08-188,922: Description of Aikawa
Toshio, "Conjugate Fiber And Fiber Sheet Using The Same." .
Derwent World Patent Database abstract of JP 04-335,060 A:
Description of Mitsui Toatsu Chem Inc (MITK), "Thermoplastic And
Decomposable Polymer Composition For Packaging." .
American Society for Testing Materials (ASTM) Designation: D
1238-95, "Standard Test Method for Flow Rates of Thermoplastics by
Extrusion Plastometer,"pp. 273-281, published Jan. 1996. .
American Society for Testing Materials (ASTM) Designation: D
5338-92, "Standard Test Method for Determining Aerobic
Biodegradation of Plastic Materials Under Controlled Composting
Conditions,"pp. 456-461, published Feb. 1993. .
Good, Robert J. and Robert R. Stromberg, Editors, "Surface and
Colloid Science-Experimental Methods," vol. II, Plenum Press, New
York, 1979, pp. 63-70..
|
Primary Examiner: Short; Patricia A.
Attorney, Agent or Firm: Connelly; Thomas J.
Parent Case Text
This application claims priority from U.S. Provisional Application
Ser. No. 60/033,952 filed on Dec. 31, 1996.
Claims
What is claimed is:
1. A thermoplastic composition comprising:
a. an aliphatic polyester polymer in a weight amount that is
between about 45 to about 90 weight percent, wherein the aliphatic
polyester polymer forms a substantially continuous phase;
b. polyolefin microfibers in a weight amount that is between
greater than 0 to about 45 weight percent, wherein the polyolefin
microfibers have a diameter that is less than about 50 micrometers
and the polyolefin microfibers form a substantially discontinuous
phase encased within the aliphatic polyester polymer substantially
continuous phase; and
c. a compatibilizer, which exhibits a hydrophilic-lipophilic
balance ratio that is between about 10 to about 40, in a weight
amount that is between about 7 to about 25 weight percent, wherein
all weight percents are based on the total weight amount of the
aliphatic polyester polymer; the polyolefin microfibers, and the
compatibilizer present in the thermoplastic composition.
2. The thermoplastic composition of claim 1 wherein the aliphatic
polyester polymer is selected from the group consisting of
poly(lactic acid), polybutylene succinate, polybutylene
succinate-co-adipate, polyhydroxybutyrate-co-valerate,
polycaprolactone, sulfonated polyethylene terephthalate, mixtures
of such polymers, and copolymers of such polymers.
3. The thermoplastic composition of claim 2 wherein the aliphatic
polyester polymer is poly(lactic acid).
4. The thermoplastic composition of claim 1 wherein the polyolefin
is selected from the group consisting of homopolymers and
copolymers comprising repeating units selected from the group
consisting of ethylene, propylene, butene, pentene, hexene,
heptene, octene, 1,3-butadiene, and 2-methyl-1,3-butadiene.
5. The thermoplastic composition of claim 4 wherein the polyolefin
is selected from the group consisting of polyethylene and
polypropylene.
6. The thermoplastic composition of claim 1 wherein the polyolefin
microfibers have a diameter that is less than about 25
micrometers.
7. The thermoplastic composition of claim 1 wherein the polyolefin
microfibers are present in a weight amount that is between about 5
to about 40 weight percent.
8. The thermoplastic composition of claim 1 wherein the
compatibilizer is an ethoxylated alcohol.
9. The thermoplastic composition of claim 1 wherein the
thermoplastic composition exhibits a Receding Contact Angle value
that is less than about 55 degrees.
10. The thermoplastic composition of claim 1 wherein the aliphatic
polyester polymer is selected from the group consisting of
poly(lactic acid), polybutylene succinate, polybutylene
succinate-co-adipate, polyhydroxybutyrate-co-valerate,
polycaprolactone, sulfonated polyethylene terephthalate, mixtures
of such polymers, and copolymers of such polymers; wherein the
polyolefin is selected from the group consisting of homopolymers
and copolymers comprising repeating units selected from the group
consisting of ethylene, propylene, butene, pentene, hexene,
heptene, octene, 1,3-butadiene, and 2-methyl-1,3-butadiene and the
polyolefin microfibers are present in a weight amount that is
between about 5 to about 40 weight percent; the compatibilizer is
an ethoxylated alcohol; and the thermoplastic composition exhibits
a Receding Contact Angle value that is less than about 55
degrees.
11. The thermoplastic composition of claim 10 wherein the aliphatic
polyester polymer is poly(lactic acid) and the polyolefin is
selected from the group consisting of polyethylene and
polypropylene.
12. A multicomponent fiber prepared from a thermoplastic
composition, wherein the thermoplastic composition comprises:
a. an aliphatic polyester polymer in a weight amount that is
between about 45 to about 90 weight percent, wherein the aliphatic
polyester polymer forms a substantially continuous phase;
b. polyolefin microfibers in a weight amount that is between
greater than 0 to about 45 weight percent, wherein the polyolefin
microfibers have a diameter that is less than about 50 micrometers
and the polyolefin microfibers form a substantially discontinuous
phase encased within the aliphatic polyester polymer substantially
continuous phase; and
c. a compatibilizer, which exhibits a hydrophilic-lipophilic
balance ratio that is between about 10 to about 40, in a weight
amount that is between about 7 to about 25 weight percent, wherein
all weight percents are based on the total weight amount of the
aliphatic polyester polymer; the polyolefin microfibers, and the
compatibilizer present in the thermoplastic composition.
wherein the multicomponent fiber exhibits a Receding Contact Angle
value that is less than about 55 degrees.
13. The multicomponent fiber of claim 12 wherein the multicomponent
fiber exhibits a Heat Shrinkage value that is less than about 10
percent.
14. The multicomponent fiber of claim 12 wherein the aliphatic
polyester polymer is selected from the group consisting of
poly(lactic acid), polybutylene succinate, polybutylene
succinate-co-adipate, polyhydroxybutyrate-co-valerate,
polycaprolactone, sulfonated polyethylene terephthalate, mixtures
of such polymers, and copolymers of such polymers.
15. The multicomponent fiber of claim 14 wherein the aliphatic
polyester polymer is poly(lactic acid).
16. The multicomponent fiber of claim 12 wherein the polyolefin is
selected from the group consisting of homopolymers and copolymers
comprising repeating units selected from the group consisting of
ethylene, propylene, butene, pentene, hexene, heptene, octene,
1,3-butadiene, and 2-methyl-1,3-butadiene.
17. The multicomponent fiber of claim 16 wherein the polyolefin is
selected from the group consisting of polyethylene and
polypropylene.
18. The multicomponent fiber of claim 12 wherein the polyolefin
microfibers have a diameter that is less than about 25
micrometers.
19. The multicomponent fiber of claim 12 wherein the polyolefin
microfibers are present in a weight amount that is between about 5
to about 40 weight percent.
20. The multicomponent fiber of claim 12 wherein the compatibilizer
is an ethoxylated alcohol.
21. The multicomponent fiber of claim 12 wherein the aliphatic
polyester polymer is selected from the group consisting of
poly(lactic acid), polybutylene succinate, polybutylene
succinate-co-adipate, polyhydroxybutyrate-co-valerate,
polycaprolactone, sulfonated polyethylene terephthalate, mixtures
of such polymers, and copolymers of such polymers; wherein the
polyolefin is selected from the group consisting of homopolymers
and copolymers comprising repeating units selected from the group
consisting of ethylene, propylene, butene, pentene, hexene,
heptene, octene, 1,3-butadiene, and 2-methyl-1,3-butadiene and the
polyolefin microfibers are present in a weight amount that is
between about 5 to about 40 weight percent; the compatibilizer is
an ethoxylated alcohol; and the multicomponent fiber exhibits a
Heat Shrinkage value that is less than about 10 percent.
22. The multicomponent fiber of claim 21 wherein the aliphatic
polyester polymer is poly(lactic acid) and the polyolefin is
selected from the group consisting of polyethylene and
polypropylene.
23. A disposable absorbent product comprising a liquid-permeable
topsheet, a backsheet attached to the topsheet, and an absorbent
structure positioned between the liquid-permeable topsheet and the
backsheet, wherein the backsheet comprises a multicomponent fiber
prepared from a thermoplastic composition, wherein the
thermoplastic composition comprises:
a. an aliphatic polyester polymer in a weight amount that is
between about 45 to about 90 weight percent, wherein the aliphatic
polyester polymer forms a substantially continuous phase;
b. polyolefin microfibers in a weight amount that is between
greater than 0 to about 45 weight percent, wherein the polyolefin
microfibers have a diameter that is less than about 50 micrometers
and the polyolefin microfibers form a substantially discontinuous
phase encased within the aliphatic polyester polymer substantially
continuous phase; and
c. a compatibilizer, which exhibits a hydrophilic-lipophilic
balance ratio that is between about 10 to about 40, in a weight
amount that is between about 7 to about 25 weight percent, wherein
all weight percents are based on the total weight amount of the
aliphatic polyester polymer; the polyolefin microfibers, and the
compatibilizer present in the thermoplastic composition.
wherein the multicomponent fiber exhibits a Receding Contact Angle
value that is less than about 55 degrees.
24. The disposable absorbent product of claim 23 wherein the
multicomponent fiber exhibits a Heat Shrinkage value that is less
than about 10 percent.
25. The disposable absorbent product of claim 23 wherein the
aliphatic polyester polymer is selected from the group consisting
of poly(lactic acid), polybutylene succinate, polybutylene
succinate-co-adipate, polyhydroxybutyrate-co-valerate,
polycaprolactone, sulfonated polyethylene terephthalate, mixtures
of such polymers, and copolymers of such polymers.
26. The disposable absorbent product of claim 25 wherein the
aliphatic polyester polymer is poly(lactic acid).
27. The disposable absorbent product of claim 23 wherein the
polyolefin is selected from the group consisting of homopolymers
and copolymers comprising repeating units selected from the group
consisting of ethylene, propylene, butene, pentene, hexene,
heptene, octene, 1,3-butadiene, and 2-methyl-1,3-butadiene.
28. The disposable absorbent product of claim 27 wherein the
polyolefin is selected from the group consisting of polyethylene
and polypropylene.
29. The disposable absorbent product of claim 23 wherein the
polyolefin microfibers have a diameter that is less than about 25
micrometers.
30. The disposable absorbent product of claim 23 wherein the
polyolefin microfibers are present in a weight amount that is
between about 5 to about 40 weight percent.
31. The disposable absorbent product of claim 23 wherein the
compatibilizer is an ethoxylated alcohol.
32. The disposable absorbent product of claim 23 wherein the
aliphatic polyester polymer is selected from the group consisting
of poly(lactic acid), polybutylene succinate, polybutylene
succinate-co-adipate, polyhydroxybutyrate-co-valerate,
polycaprolactone, sulfonated polyethylene terephthalate, mixtures
of such polymers, and copolymers of such polymers; wherein the
polyolefin is selected from the group consisting of homopolymers
and copolymers comprising repeating units selected from the group
consisting of ethylene, propylene, butene, pentene, hexene,
heptene, octene, 1,3-butadiene, and 2-methyl-1,3-butadiene and the
polyolefin microfibers are present in a weight amount that is
between about 5 to about 40 weight percent; the compatibilizer is
an ethoxylated alcohol; and the multicomponent fiber exhibits a
Heat Shrinkage value that is less than about 10 percent.
33. The disposable absorbent product of claim 32 wherein the
aliphatic polyester polymer is poly(lactic acid) and the polyolefin
is selected from the group consisting of polyethylene and
polypropylene.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multicomponent fiber. The
multicomponent fiber comprises an unreacted mixture of an aliphatic
polyester polymer as a continuous phase, polyolefin microfibers as
a discontinuous phase encased within the aliphatic polyester
polymer continuous phase, and a compatibilizer for the aliphatic
polyester polymer and the polyolefin microfibers. The
multicomponent fiber exhibits substantial biodegradable properties
yet is easily processed. The multicomponent fiber is useful in
making nonwoven structures that may be used in a disposable
absorbent product intended for the absorption of fluids such as
body fluids.
2. Description of the Related Art
Disposable absorbent products currently find widespread use in many
applications. For example, in the infant and child care areas,
diapers and training pants have generally replaced reusable cloth
absorbent articles. Other typical disposable absorbent products
include feminine care products such as sanitary napkins or tampons,
adult incontinence products, and health care products such as
surgical drapes or wound dressings. A typical disposable absorbent
product generally comprises a composite structure including a
topsheet, a backsheet, and an absorbent structure between the
topsheet and backsheet. These products usually include some type of
fastening system for fitting the product onto the wearer.
Disposable absorbent products are typically subjected to one or
more liquid insults, such as of water, urine, menses, or blood,
during use. As such, the outer cover backsheet materials of the
disposable absorbent products are typically made of
liquid-insoluble and liquid impermeable materials, such as
polypropylene films, that exhibit a sufficient strength and
handling capability so that the disposable absorbent product
retains its integrity during use by a wearer and does not allow
leakage of the liquid insulting the product.
Although current disposable baby diapers and other disposable
absorbent products have been generally accepted by the public,
these products still have need of improvement in specific areas.
For example, many disposable absorbent products can be difficult to
dispose of. For example, attempts to flush many disposable
absorbent products down a toilet into a sewage system typically
lead to blockage of the toilet or pipes connecting the toilet to
the sewage system. In particular, the outer cover materials
typically used in the disposable absorbent products generally do
not disintegrate or disperse when flushed down a toilet so that the
disposable absorbent product cannot be disposed of in this way. If
the outer cover materials are made very thin in order to reduce the
overall bulk of the disposable absorbent product so as to reduce
the likelihood of blockage of a toilet or a sewage pipe, then the
outer cover material typically will not exhibit sufficient strength
to prevent tearing or ripping as the outer cover material is
subjected to the stresses of normal use by a wearer.
Furthermore, solid waste disposal is becoming an ever increasing
concern throughout the world. As landfills continue to fill up,
there has been an increased demand for material source reduction in
disposable products, the incorporation of more recyclable and/or
degradable components in disposable products, and the design of
products that can be disposed of by means other than by
incorporation into solid waste disposal facilities such as
landfills.
As such, there is a need for new materials that may be used in
disposable absorbent products that generally retain their integrity
and strength during use, but after such use, the materials may be
more efficiently disposed of. For example, the disposable absorbent
product may be easily and efficiently disposed of by composting.
Alternatively, the disposable absorbent product may be easily and
efficiently disposed of to a liquid sewage system wherein the
disposable absorbent product is capable of being degraded.
Although degradable monocomponent fibers are known, problems have
been encountered with their use. In particular, known degradable
fibers typically do not have good thermal dimensional stability
such that the fibers usually undergo severe heat-shrinkage due to
the polymer chain relaxation during downstream heat treatment
processes such as thermal bonding or lamination.
In contrast, polyolefin materials, such as polypropylene, typically
exhibit good thermal dimensional stability but also have problems
associated with their use. In particular, polyolefin fibers
typically are hydrophobic and, and such, exhibit poor wettability,
thus limiting their use in disposable absorbent products intended
for the absorption of fluids such as body fluids. Although
surfactants can be used to improve the wettability of polyolefin
fibers, the use of such surfactants introduces additional problems
such as added cost, fugitivity or permanence, and toxicity.
Furthermore, polyolefin fibers are generally not biodegradable or
compostable.
It would therefore be desirable to prepare a fiber that exhibits
the thermal dimensional stability of polyolefin materials yet is
substantially biodegradable and is wettable without the use of
surfactants. A simple solution to this desire would be to simply
mix a polyolefin material with a degradable material so as to gain
the benefits of using both materials. However, the components of a
multicomponent fiber generally need to be chemically compatible, so
that the components effectively adhere to each other, and have
similar rheological characteristics, so that the multicomponent
fiber exhibits minimum strength and other mechanical and processing
properties. It has therefore proven to be a challenge to those
skilled in the art to combine components that meet these basic
processing needs as well as meeting the desire that the entire
multicomponent fiber be effectively substantially degradable and
hydrophilic.
It is therefore an object of the present invention to provide a
multicomponent fiber which is substantially degradable in the
environment.
It is also an object of the present invention to provide a
substantially degradable multicomponent fiber which has good
thermal dimensional stability and is hydrophilic without the
substantial use of surfactants.
It is also an object of the present invention to provide a
substantially degradable multicomponent fiber which is easily and
efficiently prepared and which is suitable for use in preparing
nonwoven structures.
SUMMARY OF THE INVENTION
The present invention concerns a thermoplastic composition that is
substantially biodegradable and yet which is easily prepared and
readily processable into desired final structures, such as fibers
or nonwoven structures.
One aspect of the present invention concerns a thermoplastic
composition that comprises a mixture of a first component, a second
component, and a third component.
One embodiment of such a thermoplastic composition comprises an
unreacted mixture of an aliphatic polyester polymer as a
substantially continuous phase, polyolefin microfibers as a
substantially discontinuous phase encased within the aliphatic
polyester polymer substantially continuous phase, and a
compatibilizer for the aliphatic polyester polymer and the
polyolefin microfibers.
In another aspect, the present invention concerns a multicomponent
fiber that is substantially degradable and yet which is easily
prepared and readily processable into desired final structures,
such as fibers or nonwoven structures.
One aspect of the present invention concerns a multicomponent fiber
that comprises an unreacted mixture of an aliphatic polyester
polymer as a substantially continuous phase, polyolefin microfibers
as a substantially discontinuous phase encased within the aliphatic
polyester polymer substantially continuous phase, and a
compatibilizer for the aliphatic polyester polymer and the
polyolefin microfibers.
In another aspect, the present invention concerns a nonwoven
structure comprising the multicomponent fiber disclosed herein.
One embodiment of such a nonwoven structure is a backsheet useful
in a disposable absorbent product.
In another aspect, the present invention concerns a disposable
absorbent product comprising the multicomponent fiber disclosed
herein.
In another aspect, the present invention concerns a process for
preparing the multicomponent fiber disclosed herein.
DETAILED DESCRIPTION OF THE PERFERRED EMBODIMENTS
The present invention is directed to a thermoplastic composition
which includes a first component, a second component, and a third
component. As used herein, the term "thermoplastic" is meant to
refer to a material that softens when exposed to heat and
substantially returns to its original condition when cooled to room
temperature.
It has been discovered that, by using an unreacted mixture of an
aliphatic polyester polymer as a substantially continuous phase,
polyolefin microfibers as a substantially discontinuous phase
encased within the aliphatic polyester polymer substantially
continuous phase, and a compatibilizer for the aliphatic polyester
polymer and the polyolefin microfibers, a thermoplastic composition
may be prepared wherein such thermoplastic composition is
substantially degradable yet which thermoplastic composition is
easily processable into fibers and nonwoven structures that exhibit
effective fibrous mechanical properties and liquid handling
properties.
The first component in the thermoplastic composition is an
aliphatic polyester polymer. Suitable aliphatic polyester polymers
include, but are not limited to, poly(lactic acid), polybutylene
succinate, polybutylene succinate-co-adipate,
polyhydroxybutyrate-co-valerate, polycaprolactone, sulfonated
polyethylene terephthalate, mixtures of such polymers, or
copolymers of such polymers.
In one embodiment of the present invention, it is desired that the
aliphatic polyester polymer used is poly(lactic acid). Poly(lactic
acid) polymer is generally prepared by the polymerization of lactic
acid. However, it will be recognized by one skilled in the art that
a chemically equivalent material may also be prepared by the
polymerization of lactide. As such, as used herein, the term
"poly(lactic acid) polymer" is intended to represent the polymer
that is prepared by either the polymerization of lactic acid or
lactide.
Lactic acid and lactide are known to be asymmetrical molecules,
having two optical isomers referred to, respectively, as the
levorotatory (hereinafter referred to as "L") enantiomer and the
dextrorotatory (hereinafter referred to as "D") enantiomer. As a
result, by polymerizing a particular enantiomer or by using a
mixture of the two enantiomers, it is possible to prepare different
polymers that are chemically similar yet which have different
properties. In particular, it has been found that by modifying the
stereochemistry of a poly(lactic acid) polymer, it is possible to
control, for example, the melting temperature, melt rheology, and
crystallinity of the polymer. By being able to control such
properties, it is possible to prepare a multicomponent fiber
exhibiting desired melt strength, mechanical properties, softness,
and processability properties so as to be able to make attenuated,
heat set, and crimped fibers.
It is generally desired that the aliphatic polyester polymer be
present in the thermoplastic composition in an amount effective to
result in the thermoplastic composition exhibiting desired
properties. The aliphatic polyester polymer will be present in the
thermoplastic composition in a weight amount that is less than 100
weight percent, beneficially between about 45 weight percent to
about 90 weight percent, suitably between about 50 weight percent
to about 88 weight percent, and more suitably between about 55
weight percent to about 70 weight percent, wherein all weight
percents are based on the total weight amount of the aliphatic
polyester polymer, the polyolefin microfiber, and the
compatibilizer present in the thermoplastic composition. The
compositional ratio of the three components in the thermoplastic
composition is generally important to maintaining the substantial
biodegradability of the thermoplastic composition because the
aliphatic polyester polymer generally needs to be in a
substantially continuous phase in order to maintain access to the
biodegradable portion of the thermoplastic composition. An
approximation of the limits of component ratios can be determined
based on the densities of the components. The density of a
component is converted to a volume (assume 100 g of each
component), the volumes of the components are added together for a
total thermoplastic composition volume and the components' weight
averages calculated to establish the approximate minimum ratio of
each component needed to produce a thermoplastic composition with a
volumetric majority of the aliphatic polyester polymer in the
blend.
It is generally desired that the aliphatic polyester polymer
exhibit a weight average molecular weight that is effective for the
thermoplastic composition to exhibit desirable melt strength, fiber
mechanical strength, and fiber spinning properties. In general, if
the weight average molecular weight of an aliphatic polyester
polymer is too high, this represents that the polymer chains are
heavily entangled which may result in a thermoplastic composition
comprising that aliphatic polyester polymer being difficult to
process. Conversely, if the weight average molecular weight of an
aliphatic polyester polymer is too low, this represents that the
polymer chains are not entangled enough which may result in a
thermoplastic composition comprising that aliphatic polyester
polymer exhibiting a relatively weak melt strength, making high
speed processing very difficult. Thus, aliphatic polyester polymers
suitable for use in the present invention exhibit weight average
molecular weights that are beneficially between about 10,000 to
about 2,000,000, more beneficially between about 50,000 to about
400,000, and suitably between about 100,000 to about 300,000. The
weight average molecular weight for polymers or polymer blends can
be determined using a method as described in the Test Methods
section herein.
It is also desired that the aliphatic polyester polymer exhibit a
polydispersity index value that is effective for the thermoplastic
composition to exhibit desirable melt strength, fiber mechanical
strength, and fiber spinning properties. As used herein,
"polydispersity index" is meant to represent the value obtained by
dividing the weight average molecular weight of a polymer by the
number average molecular weight of the polymer. In general, if the
polydispersity index value of an aliphatic polyester polymer is too
high, a thermoplastic composition comprising that aliphatic
polyester polymer may be difficult to process due to inconsistent
processing properties caused by polymer segments comprising low
molecular weight polymers that have lower melt strength properties
during spinning. Thus, it is desired that the aliphatic polyester
polymer exhibits a polydispersity index value that is beneficially
between about 1 to about 15, more beneficially between about 1 to
about 4, and suitably between about 1 to about 3. The number
average molecular weight for polymers or polymer blends can be
determined using a method as described in the Test Methods section
herein.
In the present invention, it is desired that the aliphatic
polyester polymer be biodegradable. As a result, the thermoplastic
composition comprising the aliphatic polyester polymer, either in
the form of a fiber or in the form of a nonwoven structure, will be
substantially degradable when disposed of to the environment and
exposed to air and/or water. As used herein, "biodegradable" is
meant to represent that a material degrades from the action of
naturally occurring microorganisms such as bacteria, fungi, and
algae.
In the present invention, it is also desired that the aliphatic
polyester polymer be compostable. As a result, the thermoplastic
composition comprising the aliphatic polyester polymer, either in
the form of a fiber or in the form of a nonwoven structure, will be
substantially compostable when disposed of to the environment and
exposed to air and/or water. As used herein, "compostable" is meant
to represent that a material is capable of undergoing biological
decomposition in a compost site such that the material is not
visually distinguishable and breaks down into carbon dioxide,
water, inorganic compounds, and biomass, at a rate consistent with
known compostable materials.
The second component in the thermoplastic composition is polyolefin
microfibers. Polyolefins are known to those skilled in the art. Any
polyolefin capable of being fabricated into an article, such as a
microfiber, is believed suitable for use in the present invention.
Exemplary of polyolefins suitable for use in the present invention
are the homopolymers and copolymers comprising repeating units
formed from one or more aliphatic hydrocarbons, including ethylene,
propylene, butene, pentene, hexene, heptene, octene, 1,3-butadiene,
and 2-methyl-1,3-butadiene. The polyolefins may be high or low
density and may be generally linear or branched chain polymers.
Methods of forming polyolefins are known to those skilled in the
art.
Polyolefins, such as those described above, are generally
hydrophobic in nature. As used herein, the term "hydrophobic"
refers to a material having a contact angle of water in air of at
least 90 degrees. In contrast, as used herein, the term
"hydrophilic" refers to a material having a contact angle of water
in air of less than 90 degrees. For the purposes of this
application, contact angle measurements may be determined as set
forth in Robert J. Good and Robert J. Stromberg, Ed., in "Surface
and Colloid Science--Experimental Methods", Vol. II, (Plenum Press,
1979), pages 63-70.
It is generally desired that both the aliphatic polyester polymer
and the polyolefin be melt processable. It is therefore desired
that the aliphatic polyester polymer and the polyolefin exhibit a
melt flow rate that is beneficially between about 1 gram per 10
minutes to about 200 grams per 10 minutes, suitably between about
10 grams per 10 minutes to about 100 grams per 10 minutes, and more
suitably between about 20 grams per 10 minutes to about 40 grams
per 10 minutes. The melt flow rate of a material may be determined
according to ASTM Test Method D1238-E incorporated in its entirety
herein by reference.
In the present invention, the polyolefin is used in the form of a
microfiber. As used herein, the term "microfiber" is meant to refer
to a fibrous material having a diameter that is less than about 50
micrometers, beneficially less than about 25 micrometers more
beneficially less than about 10 micrometers, suitably less than
about 5 micrometers, and most suitably less than about 1
micrometer.
In one embodiment of the present invention, the polyolefin
microfiber comprises a percentage of the cross sectional area of a
multicomponent fiber prepared from the thermoplastic composition of
the present invention that is effective for the multicomponent
fiber to exhibit desirable melt strength, fiber mechanical
strength, and fiber spinning properties. In general, if the
polyolefin microfiber comprises a percentage of the cross sectional
area of a multicomponent fiber that is too high, this generally
results in a multicomponent fiber that will not be substantially
biodegradable or that will be difficult to process. Conversely, if
the polyolefin microfiber comprises a percentage of the cross
sectional area of a multicomponent fiber that is too low, this
generally results in a multicomponent fiber that will not exhibit
effective structural properties or that may be difficult to
process. Thus, the polyolefin microfiber desirably comprises a
percentage of the cross sectional area of a multicomponent fiber
that is beneficially less than about 20 percent of the cross
sectional area of the multicomponent fiber, more beneficially less
than about 15 percent of the cross sectional area of the
multicomponent fiber, and suitably less than about 10 percent of
the cross sectional area of the multicomponent fiber.
As used herein, the term "fiber" or "fibrous" is meant to refer to
a material wherein the length to diameter ratio of such material is
greater than about 10. Conversely, a "nonfiber" or "nonfibrous"
material is meant to refer to a material wherein the length to
diameter ratio of such material is about 10 or less.
The polyolefin is generally desired to be in the form of a
microfiber so as to allow the polyolefin to effectively function as
a structural support within the thermoplastic composition so as to
prevent a substantial thermal dimensional-shrinkage of the
thermoplastic composition during processing while generally
maintaining a desired degree of substantial biodegradability of the
thermoplastic composition.
It is generally desired that the polyolefin microfibers be present
in the thermoplastic composition in an amount effective to result
in the thermoplastic composition exhibiting desired properties. The
polyolefin microfibers will be present in the thermoplastic
composition in a weight amount that is beneficially between greater
than 0 weight percent to about 45 weight percent, suitably between
about 5 weight percent to about 40 weight percent, and more
suitably between about 10 weight percent to about 30 weight
percent, wherein all weight percents are based on the total weight
amount of the aliphatic polyester polymer, the polyolefin
microfiber, and the compatibilizer present in the thermoplastic
composition. It is generally important for the polyolefin to be a
substantially discontinuous phase of the thermoplastic composition
so that the polyolefin microfibers can provide structural support
to the thermoplastic composition or materials formed from the
thermoplastic composition, such as fibers or nonwovens, without
negatively affecting the biodegradability of the aliphatic
polyester or of the substantial biodegradability of the
thermoplastic composition or materials formed from the
thermoplastic composition.
Either separately or when mixed together, the aliphatic polyester
polymer and the polyolefin microfiber are generally hydrophobic.
However, it is generally desired that the thermoplastic composition
of the present invention, and fibers prepared from the
thermoplastic composition, generally be hydrophilic so that such
fibers are useful in disposable absorbent products which are
insulted with aqueous liquids such as water, urine, menses, or
blood. Thus, it has been found desirable to use another component
as a surfactant in the thermoplastic composition of the present
invention in order to achieve the desired hydrophilic
properties.
Furthermore, it has been found desirable to improve the
processability of the aliphatic polyester polymer and the
polyolefin microfibers, since such polymers are not chemically
identical and are, therefore, somewhat incompatible with each other
which tends to negatively affect the processing of a mixture of
such polymers. For example, the aliphatic polyester polymer and the
polyolefin microfibers are sometimes difficult to effectively mix
and prepare as an essentially homogeneous mixture on their own.
Generally, then, it has been found desirable to use a
compatibilizer to aid in the effective preparation and processing
of the aliphatic polyester polymer and the polyolefin microfibers
into a single thermoplastic composition.
Therefore, the third component in the thermoplastic composition is
a compatibilizer for the aliphatic polyester polymer and the
polyolefin microfibers. Compatibilizers suitable for use in the
present invention will generally comprise a hydrophilic section
which will generally be compatible to the aliphatic polyester
polymer and a hydrophobic section which will generally be
compatible to the polyolefin microfibers. These hydrophilic and
hydrophobic sections will generally exist in separate blocks so
that the overall compatibilizer structure may be di-block or random
block. It is generally desired that the compatibilizer initially
functions as a plasticizer in order to improve the preparation and
processing of the thermoplastic composition. It is then generally
desired that the compatibilizer serves as a surfactant in a
material processed from the thermoplastic composition, such as a
fiber or nonwoven structure, by modifying the contact angle of
water in air of the processed material. The hydrophobic portion of
the compatibilizer may be, but is not limited to, a polyolefin such
as polyethylene or polypropylene. The hydrophilic portion of the
compatibilizer may contain ethylene oxide, ethoxylates, glycols,
alcohols or any combinations thereof. Examples of suitable
compatibilizers include UNITHOX.RTM.480 and UNITHOX.RTM.750
ethoxylated alcohols, or UNICID.RTM. Acid Amide Ethoxylates, all
available from Petrolite Corporation of Tulsa, Okla.
It is generally desired that the compatibilizer exhibit a weight
average molecular weight that is effective for the thermoplastic
composition to exhibit desirable melt strength, fiber mechanical
strength, and fiber spinning properties. In general, if the weight
average molecular weight of a compatibilizer is too high, the
compatibilizer will not blend well with the other components in the
thermoplastic composition because the compatibilizer's viscosity
will be so high that it lacks the mobility needed to blend.
Conversely, if the weight average molecular weight of the
compatibilizer is too low, this represents that the compatibilizer
will generally not blend well with the other components and have
such a low viscosity that it causes processing problems. Thus,
compatibilizers suitable for use in the present invention exhibit
weight average molecular weights that are beneficially between
about 1,000 to about 100,000, suitably between about 1,000 to about
50,000, and more suitably between about 1,000 to about 10,000. The
weight average molecular weight for a compatibilizer material can
be determined using methods known to those skilled in the art.
It is generally desired that the compatibilizer exhibit an
effective hydrophilic-lipophilic balance ratio (HLB ratio). The HLB
ratio of a material describes the relative ratio of the
hydrophilicity of the material. The HLB ratio is calculated as the
weight average molecular weight of the hydrophilic portion divided
by the total weight average molecular weight of the material, which
value is then multiplied by 20. If the HLB ratio value is too low,
the material will generally not provide the desired improvement in
hydrophilicity. Conversely, if the HLB ratio value is too high, the
material will generally not blend into the thermoplastic
composition because of chemical incompatibility and differences in
viscosities with the other components. Thus, compatibilizers useful
in the present invention exhibit HLB ratio values that are
beneficially between about 10 to about 40, suitably between about
10 to about 20, and more suitably between about 12 to about 18.
It is generally desired that the compatibilizer be present in the
thermoplastic composition in an amount effective to result in the
thermoplastic composition exhibiting desired properties. In
general, a minimal amount of the compatibilizer will be needed to
achieve an effective blending and processing with the other
components in the thermoplastic composition. In general, too much
of the compatibilizer will lead to processing problems of the
thermoplastic composition. The compatibilizer will be present in
the thermoplastic composition in a weight amount that is
beneficially between about 7 weight percent to about 25 weight
percent, more beneficially between about 10 weight percent to about
25 weight percent, suitably between about 12 weight percent to
about 20 weight percent, and more suitably between about 13 weight
percent to about 18 weight percent, wherein all weight percents are
based on the total weight amount of the aliphatic polyester
polymer, the polyolefin microfiber, and the compatibilizer present
in the thermoplastic composition.
While the principal components of the thermoplastic composition of
the present invention have been described in the foregoing, such
thermoplastic composition is not limited thereto and can include
other components not adversely effecting the desired properties of
the thermoplastic composition. Exemplary materials which could be
used as additional components would include, without limitation,
pigments, antioxidants, stabilizers, surfactants, waxes, flow
promoters, solid solvents, plasticizers, nucleating agents,
particulates, and materials added to enhance processability of the
thermoplastic composition. If such additional components are
included in a thermoplastic composition, it is generally desired
that such additional components be used in an amount that is
beneficially less than about 5 weight percent, more beneficially
less than about 3 weight percent, and suitably less than about 1
weight percent, wherein all weight percents are based on the total
weight amount of the aliphatic polyester polymer, the polyolefin
microfiber, and the compatibilizer present in the thermoplastic
composition.
The thermoplastic composition of the present invention is generally
simply a mixture of the aliphatic polyester polymer, the polyolefin
microfibers, the compatibilizer, and, optionally, any additional
components. In order to achieve the desired properties for the
thermoplastic composition of the present invention, it is desirable
that the aliphatic polyester polymer, the polyolefin microfibers,
and the compatibilizer remain substantially unreacted with each
other. As such, each of the aliphatic polyester polymer, the
polyolefin microfibers, and the compatibilizer remain distinct
components of the thermoplastic composition. Furthermore, it is
desired that the aliphatic polyester polymer form a substantially
continuous phase and that the polyolefin microfibers form a
substantially discontinuous phase, wherein the aliphatic polyester
polymer continuous phase substantially encases the polyolefin
microfibers within its structure. As used herein, the term
"encase", and related terms, are intended to mean that the
aliphatic polyester polymer continuous phase substantially encloses
or surrounds the polyolefin microfibers.
In one embodiment of the present invention, after dry mixing
together the aliphatic polyester polymer, the polyolefin
microfibers, and the compatibilizer to form a thermoplastic
composition dry mixture, such thermoplastic composition dry mixture
is beneficially agitated, stirred, or otherwise blended to
effectively uniformly mix the aliphatic polyester polymer, the
polyolefin microfibers, and the compatibilizer such that an
essentially homogeneous dry mixture is formed. The dry mixture may
then be melt blended in, for example, an extruder, to effectively
uniformly mix the aliphatic polyester polymer, the polyolefin
microfibers, and the compatibilizer such that an essentially
homogeneous melted mixture is formed. The essentially homogeneous
melted mixture may then be cooled and pelletized. Alternatively,
the essentially homogeneous melted mixture may be sent directly to
a spin pack or other equipment for forming fibers or a nonwoven
structure.
Alternative methods of mixing together the components of the
present invention include first mixing together the aliphatic
polyester polymer and the polyolefin microfibers and then adding
the compatibilizer to such a mixture in, for example, an extruder
being used to mix the components together. In addition, it is also
possible to initially melt mix all of the components together at
the same time. Other methods of mixing together the components of
the present invention are also possible and will be easily
recognized by one skilled in the art.
The present invention is also directed to a multicomponent fiber
which is prepared from the thermoplastic composition of the present
invention. For purposes of illustration only, the present invention
will generally be described in terms of a multicomponent fiber
comprising only three components. However, it should be understood
that the scope of the present invention is meant to include fibers
with three or more components. In one embodiment, the thermoplastic
composition of the present invention may be used to form the sheath
of a multicomponent fiber while a polyolefin, such as polypropylene
or polyethylene, is used to form the core. Suitable structural
geometries for multicomponent fibers include pie shape or side by
side configurations.
With the aliphatic polyester polymer forming a substantially
continuous phase, the aliphatic polyester polymer will generally
provide an exposed surface on at least a portion of the
multicomponent fiber which will generally permit thermal bonding of
the multicomponent fiber to other fibers which may be the same or
different from the multicomponent fiber of the present invention.
As a result, the multicomponent fiber can then be used to form
thermally bonded fibrous nonwoven structures such as a nonwoven
web. The polyolefin microfibers in the multicomponent fiber
generally provide strength or rigidity to the multicomponent fiber
and, thus, to any nonwoven structure comprising the multicomponent
fiber. In order to provide such strength or rigidity to the
multicomponent fiber, it is generally desired that the polyolefin
microfibers be substantially continuous along the length of the
multicomponent fiber.
Typical conditions for thermally processing the various components
include using a shear rate that is beneficially between about 100
seconds.sup.-1 to about 10000 seconds.sup.-1, more beneficially
between about 500 seconds.sup.-1 to about 5000 seconds.sup.-1,
suitably between about 1000 seconds.sup.-1 to about 2000
seconds.sup.-1, and most suitably at about 1000 seconds.sup.-1.
Typical conditions for thermally processing the components also
include using a temperature that is beneficially between about
100.degree. C. to about 500.degree. C., more beneficially between
about 150.degree. C. to about 300.degree. C., and suitably between
about 175.degree. C. to about 250.degree. C.
Methods for making multicomponent fibers are well known and need
not be described here in detail. The melt spinning of polymers
includes the production of continuous filament, such as spunbond or
meltblown, and non-continuous filament, such as staple and
short-cut fibers, structures. To form a spunbond or meltblown
fiber, generally, a thermoplastic composition is extruded and fed
to a distribution system where the thermoplastic composition is
introduced into a spinneret plate. The spun fiber is then cooled,
solidified, and drawn by an aerodynamic system, to be formed into a
conventional nonwoven. Meanwhile, to produce short-cut or staple
fiber, rather than being directly formed into a nonwoven structure,
the spun fiber is cooled, solidified, and drawn, generally by a
mechanical rolls system, to an intermediate filament diameter and
collected. Subsequently, the fiber may be "cold drawn" at a
temperature below its softening temperature, to the desired
finished fiber diameter and crimped or texturized and cut into a
desirable fiber length.
The process of cooling an extruded thermoplastic composition to
ambient temperature is usually achieved by blowing ambient or
sub-ambient temperature air over the extruded thermoplastic
composition. It can be referred to as quenching or super-cooling
because the change in temperature is usually greater than
100.degree. C. and most often greater than 150.degree. C. over a
relatively short time frame, such as in seconds.
Multicomponent fibers can be cut into relatively short lengths,
such as staple fibers which generally have lengths in the range of
about 25 to about 50 millimeters and short-cut fibers which are
even shorter and generally have lengths less than about 18
millimeters. See, for example, U.S. Pat. No. 4,789,592 to Taniguchi
et al, and U.S. Pat. No. 5,336,552 to Strack et al., both of which
are incorporated herein by reference in their entirety.
The resultant multicomponent fibers of the present invention are
desired to exhibit an improvement in hydrophilicity, evidenced by a
decrease in the contact angle of water in air. The contact angle of
water in air of a fiber sample can be measured as either an
advancing or a receding contact angle value because of the nature
of the testing procedure. The advancing contact angle generally
measures a material's initial response to a liquid, such as water.
The receding contact angle generally gives a measure of how a
material will perform over the duration of a first insult, or
exposure to liquid, as well as over following insults. A lower
receding contact angle means that the material is becoming more
hydrophilic during the liquid exposure and will generally then be
able to transport liquids more consistently. The receding contact
angle data is used to establish the highly hydrophilic nature of a
multicomponent fiber of the present invention although it is
preferable that a decrease in the advancing contact angle of the
multicomponent fiber also takes place.
Thus, in one embodiment of the present invention, it is desired
that the thermoplastic composition or a multicomponent fiber
exhibit a Receding Contact Angle value that is beneficially less
than about 55 degrees, more beneficially less than about 40
degrees, suitably less than about 25 degrees, more suitably less
than about 20 degrees, and most suitably less than about 10
degrees, wherein the receding contact angle is determined by the
method that is described in the Test Methods section herein.
Typical aliphatic polyester-based materials often undergo heat
shrinkage during downstream thermal processing. The heat-shrinkage
mainly occurs due to the thermally-induced chain relaxation of the
polymer segments in the amorphous phase and incomplete crystalline
phase. To overcome this problem, it is generally desirable to
maximize the crystallization of the material before the bonding
stage so that the thermal energy goes directly to melting rather
than to allow for chain relaxation and reordering of the incomplete
crystalline structure. The typical solution to this problem is to
subject the material to a heat-setting treatment. As such, when
prepared materials, such as fibers, are subjected to heat-setting
upon reaching a bonding roll, the fibers won't substantially shrink
because such fibers are already fully or highly oriented. The
present invention alleviates the need for this additional
processing step because of the morphology of the multicomponent
fiber of the present invention. As discussed earlier, the
polyolefin microfibers generally provide a reinforcing structure
which minimizes the expected heat shrinkage of the aliphatic
polyester.
In one embodiment of the present invention, it is desired that the
thermoplastic composition or a multicomponent fiber exhibit an
amount of shrinking, as quantified by a Heat Shrinkage value, at a
temperature of about 100.degree. C., that is beneficially less than
about 10 percent, more beneficially less than about 5 percent,
suitably less than about 2 percent, and more suitably less than
about 1 percent, wherein the amount of shrinking is based upon the
difference between the initial and final lengths of a fiber divided
by the initial length multiplied by 100. The method by which the
amount of shrinking that a fiber exhibits may be determined is
included in the Test Methods section herein.
The multicomponent fibers of the present invention are suited for
use in disposable products including disposable absorbent products
such as diapers, adult incontinent products, and bed pads; in
catamenial devices such as sanitary napkins, and tampons; and other
absorbent products such as wipes, bibs, wound dressings, and
surgical capes or drapes. Accordingly, in another aspect, the
present invention relates to a disposable absorbent product
comprising the multicomponent fibers of the present invention.
In one embodiment of the present invention, the multicomponent
fibers are formed into a fibrous matrix for incorporation into a
disposable absorbent product. A fibrous matrix may take the form
of, for example, a fibrous nonwoven web. Fibrous nonwoven webs may
be made completely from the multicomponent fibers of the present
invention or they may be blended with other fibers. The length of
the fibers used may depend on the particular end use contemplated.
Where the fibers are to be degraded in water as, for example, in a
toilet, it is advantageous if the lengths are maintained at or
below about 15 millimeters.
In one embodiment of the present invention, a disposable absorbent
product is provided, which disposable absorbent product comprises a
liquid-permeable topsheet, a backsheet attached to the
liquid-permeable topsheet, and an absorbent structure positioned
between the liquid-permeable topsheet and the backsheet, wherein
the backsheet comprises multicomponent fibers of the present
invention.
Exemplary disposable absorbent products are generally described in
U.S. Pat. No. 4,710,187; U.S. Pat. No. 4,762,521; U.S. Pat. No.
4,770,656; and U.S. Pat. No. 4,798,603; which references are
incorporated herein by reference.
Absorbent products and structures according to all aspects of the
present invention are generally subjected, during use, to multiple
insults of a body liquid. Accordingly, the absorbent products and
structures are desirably capable of absorbing multiple insults of
body liquids in quantities to which the absorbent products and
structures will be exposed during use. The insults are generally
separated from one another by a period of time.
Test Methods
Melting Temperature
The melting temperature of a material was determined using
differential scanning calorimetry. A differential scanning
calorimeter, under the designation Thermal Analyst 2910
Differential Scanning Calorimeter, which was outfitted with a
liquid nitrogen cooling accessory and used in combination with
Thermal Analyst 2200 analysis software (version 8.10) program, both
available from T.A. Instruments Inc. of New Castle, Del., was used
for the determination of melting temperatures.
The material samples tested were either in the form of fibers or
resin pellets. It is preferred to not handle the material samples
directly, but rather to use tweezers and other tools, so as not to
introduce anything that would produce erroneous results. The
material samples were cut, in the case of fibers, or placed, in the
case of resin pellets, into an aluminum pan and weighed to an
accuracy of 0.01 mg on an analytical balance. If needed, a lid was
crimped over the material sample onto the pan.
The differential scanning calorimeter was calibrated using an
indium metal standard and a baseline correction performed, as
described in the manual for the differential scanning calorimeter.
A material sample was placed into the test chamber of the
differential scanning calorimeter for testing and an empty pan is
used as a reference. All testing was run with a 55 cubic
centimeter/minute nitrogen (industrial grade) purge on the test
chamber. The heating and cooling program is a 2 cycle test that
begins with equilibration of the chamber to -75.degree. C.,
followed by a heating cycle of 20.degree. C./minute to 220.degree.
C., followed by a cooling cycle at 20.degree. C./minute to
-75.degree. C., and then another heating cycle of 20.degree.
C./minute to 220.degree. C.
The results were evaluated using the analysis software program
wherein the glass transition temperature (Tg) of inflection,
endothermic and exothermic peaks were identified and quantified.
The glass transition temperature was identified as the area on the
line where a distinct change in slope occurs and then the melting
temperature is determined using an automatic inflection
calculation.
Apparent Viscosity
A capillary rheometer, under the designation Gottfert Rheograph
2003 capillary rheometer, which was used in combination with
WinRHEO (version 2.31) analysis software, both available from
Gottfert Company of Rock Hill, S.C., was used to evaluate the
apparent viscosity rheological properties of material samples. The
capillary rheometer setup included a 2000 bar pressure transducer
and a 30 mm length/30 mm active length/1 mm diameter/0 mm
height/180.degree. run in angle, round hole capillary die.
If the material sample being tested demonstrates or is known to
have water sensitivity, the material sample is dried in a vacuum
oven above its glass transition temperature, i.e. above 55 or
60.degree. C. for poly(lactic acid) materials, under a vacuum of at
least 15 inches of mercury with a nitrogen gas purge of at least 30
standard cubic feet per hour for at least 16 hours.
Once the instrument is warmed up and the pressure transducer is
calibrated, the material sample is loaded incrementally into the
column, packing resin into the column with a ramrod each time to
ensure a consistent melt during testing. After material sample
loading, a 2 minute melt time precedes each test to allow the
material sample to completely melt at the test temperature. The
capillary rheometer takes data points automatically and determines
the apparent viscosity (in Pascal-second) at 7 apparent shear rates
(in second.sup.-1): 50, 100, 200, 500, 1000, 2000, and 5000. When
examining the resultant curve it is important that the curve be
relatively smooth. If there are significant deviations from a
general curve from one point to another, possibly due to air in the
column, the test run should be repeated to confirm the results.
The resultant rheology curve of apparent shear rate versus apparent
viscosity gives an indication of how the material sample will run
at that temperature in an extrusion process. The apparent viscosity
values at a shear rate of at least 1000 second.sup.-1 are of
specific interest because these are the typical conditions found in
commercial fiber spinning extruders.
Molecular Weight
A gas permeation chromatography (GPC) method is used to determine
the molecular weight distribution of samples, such as of
poly(lactic acid) whose weight average molecular weight (M.sub.w)
is between about 800 to about 400,000.
The GPC is set up with two PLgel Mixed K linear 5 micron,
7.5.times.300 millimeter analytical columns in series. The column
and detector temperatures are 30.degree. C. The mobile phase is
high-performance liquid chromatography (HPLC) grade tetrahydrofuran
(THF). The pump rate is 0.8 milliliter per minute with an injection
volume of 25 microliters. Total run time is 30 minutes. It is
important to note that new analytical columns must be installed
about every 4 months, a new guard column about every month, and a
new in-line filter about every month.
Standards of polystyrene polymers, obtained from Aldrich Chemical
Co., should be mixed into a solvent of dichloromethane(DCM):THF
(10:90), both HPLC grade, in order to obtain 1 mg/mL
concentrations. Multiple polystyrene standards can be combined in
one standard solution provided that their peaks do not overlap when
chromatographed. A range of standards of about 687 to 400,000
molecular weight should be prepared. Examples of standard mixtures
with Aldrich polystyrenes of varying weight average molecular
weights include: Standard 1 (401,340; 32,660; 2,727), Standard 2
(45,730; 4,075), Standard 3 (95,800; 12,860) and Standard 4
(184,200; 24,150; 687).
Next, prepare the stock check standard. Dissolve 10 g of a 200,000
molecular weight poly(lactic acid) standard, Catalog#19245 obtained
from Polysciences Inc., to 100 ml of HPLC grade DCM to a glass jar
with a lined lid using an orbital shaker (at least 30 minutes).
Pour out the mixture onto a clean, dry, glass plate and first allow
the solvent to evaporate, then place in a 35.degree. C. preheated
vacuum oven and dry for about 14 hours under a vacuum of 25 mm of
mercury. Next, remove the poly(lactic acid) from the oven and cut
the film into small strips. Immediately grind the samples using a
grinding mill (with a 10 mesh screen) taking care not to add too
much sample and causing the grinder to freeze up. Store a few grams
of the ground sample in a dry glass jar in a dessicator, while the
remainder of the sample can be stored in the freezer in a similar
type jar.
It is important to prepare a new check standard prior to the
beginning of each new sequence and, because the molecular weight is
greatly affected by sample concentration, great care should be
taken in its weighing and preparation. To prepare the check
standard weigh out 0.0800 g .+-.0.0025 g of 200,000 weight average
molecular weight poly(lactic acid) reference standard into a clean
dry scintillation vial. Then, using a volumetric pipet or dedicated
repipet, add 2 ml of DCM to the vial and screw the cap on tightly.
Allow the sample to dissolve completely. Swirl the sample on an
orbital shaker, such as a Thermolyne Roto Mix (type 51300) or
similar mixer, if necessary. To evaluate whether is it dissolved
hold the vial up to the light at a 45.degree. angle. Turn it slowly
and watch the liquid as it flows down the glass. If the bottom of
the vial does not appear smooth, the sample is not completely
dissolved. It may take the sample several hours to dissolve. Once
dissolved, add 18 ml of THF using a volumetric pipet or dedicated
repipet, cap the vial tightly and mix.
Sample preparations begins by weighing 0.0800 g .+-.0.0025 g of the
sample into a clean, dry scintillation vial (great care should also
be taken in its weighing and preparation). Add 2 ml of DCM to the
vial with a volumetric pipet or dedicated repipet and screw the cap
on tightly. Allow the sample to dissolve completely using the same
technique described in the check standard preparation above. Then
add 18 ml of THF using a volumetric pipet or dedicated repipet, cap
the vial tightly and mix.
Begin the evaluation by making a test injection of a standard
preparation to test the system equilibration. Once equilibration is
confirmed inject the standard preparations. After those are run,
first inject the check standard preparation and then the sample
preparations. Inject the check standard preparation after every 7
sample injections and at the end of testing. Be sure not to take
any more than two injections from any one vial, and those two
injections must be made within 4.5 hours of each other.
There are 4 quality control parameters to assess the results.
First, the correlation coefficient of the fourth order regression
calculated for each standard should be not less than 0.950 and not
more than 1.050. Second, the relative standard deviation of all the
weight average molecular weights of the check standard preparations
should not be more than 5.0 percent. Third, the average of the
weight average molecular weights of the check standard preparation
injections should be within 10 percent of the weight average
molecular weight on the first check standard preparation injection.
Lastly, record the lactide response for the 200 microgram per
milliliter (.mu.g/mL) standard injection on a SQC data chart. Using
the chart's control lines, the response must be within the defined
SQC parameters.
Calculate the Molecular statistics based on the calibration curve
generated from the polystyrene standard preparations and constants
for poly(lactic acid) and polystyrene in THF at 30.degree. C. Those
are: Polystyrene (K=14.1*10.sup.5, alpha=0.700) and poly(lactic
acid) (K=54.9*10.sup.5, alpha=0.639).
Heat Shrinkage of Fibers
The required equipment for the determination of heat shrinkage
include: a convection oven (Thelco model 160DM laboratory oven,
available from Precision and Scientific Inc., of Chicago, Ill.),
0.5 g (+/-0.06 g) sinker weights, 1/2 inch binder clips, masking
tape, graph paper with at least 1/4 inch squares, foam posterboard
(11 by 14 inches) or equivalent substrate to attach the graph paper
and samples to. The convection oven should be capable of a
temperature of about 100.degree. C.
Fiber samples are melt spun at their respective spinning
conditions. In general, a 30 filament bundle is preferred and
mechanically drawn to obtain fibers with a jetstretch ratio of
beneficially 224 or higher. Only fibers of the same jetstretch
ratio can be compared to one another in regards to their heat
shrinkage. The jetstretch ratio of a fiber is the ratio of the
speed of the drawdown roll divided by the linear extrusion rate
(distance/time) of the melted polymer exiting the spinneret. The
spun fiber is usually collected onto a bobbin using a winder. The
collected fiber bundle is separated into 30 filaments, if a 30
filament bundle has not already been obtained, and cut into 9 inch
lengths.
The graph paper is taped onto the posterboard where one edge of the
graph paper is matched with the edge of the posterboard. One end of
the fiber bundle is taped, no more than the end 1 inch. The taped
end is clipped to the posterboard at the edge where the graph paper
is matched up such that the edge of the clip rests over one of the
horizontal lines on the graph paper while holding the fiber bundle
in place (the taped end should be barely visible as it is secured
under the clip). The other end of the bundle is pulled taught and
lined up parallel to the vertical lines on the graph paper. Next,
at 7 inches down from the point where the clip is binding the
fiber, pinch the 0.5 g sinker around the fiber bundle. Repeat the
attachment process for each replicate. Usually, 3 replicates can be
attached at one time. Marks can be made on the graph paper to
indicate the initial positions of the sinkers. The samples are
placed into the oven at a temperature of about 100.degree. C. such
that the samples hang vertically and do not touch the posterboard.
At time intervals of 5, 10 and 15 minutes quickly mark the new
location of the sinkers on the graph paper and return samples to
the oven.
After the testing is complete, remove the posterboard and measure
the distances between the origin (where the clip held the fibers)
and the marks at 5, 10 and 15 minutes with a ruler graduated to
1/16 inch. Three replicates per sample is recommended. Calculate
averages, standard deviations and percent shrinkage. The percent
shrinkage is calculated as (initial length--measured length)
divided by the initial length and multiplied by 100. As reported in
the examples herein and as used throughout the claims, the Heat
Shrinkage value represents the amount of heat shrinkage that a
fiber sample exhibits at a temperature of about 100.degree. C. for
a time period of about 15 minutes, as determined according to the
preceding test method.
Contact Angle
The equipment includes a DCA-322 Dynamic Contact Angle Analyzer and
WinDCA (version 1.02) software, both available from ATI-CAHN
Instruments, Inc., of Madison, Wis. Testing was done on the "A"
loop with a balance stirrup attached. Calibrations should be done
monthly on the motor and daily on the balance (100 mg mass used) as
indicated in the manual.
Thermoplastic compositions are spun into fibers and the freefall
sample (jetstretch of 0) is used for the determination of contact
angle. Care should be taken throughout fiber preparation to
minimize fiber exposure to handling to ensure that contamination is
kept to a minimum. The fiber sample is attached to the wire hanger
with scotch tape such that 2-3 cm of fiber extends beyond the end
of the hanger. Then the fiber sample is cut with a razor so that
1.5 cm is extending beyond the end of the hanger. An optical
microscope is used to determine the average diameter (3 to 4
measurements) along the fiber.
The sample on the wire hanger is suspended from the balance stirrup
on loop "A". The immersion liquid is distilled water and it is
changed for each specimen. The specimen parameters are entered
(i.e. fiber diameter) and the test started. The stage advances at
151.75 microns/second until it detects the Zero Depth of Immersion
when the fiber contacts the surface of the distilled water. From
the Zero Depth of Immersion, the fiber advances into the water for
1 cm, dwells for 0 seconds and then immediately recedes 1 cm. The
auto-analysis of the contact angle done by the software determines
the advancing and receding contact angles of the fiber sample based
on standard calculations identified in the manual. Contact angles
of 0 or <0 indicate that the sample has become totally wettable.
Five replicates for each sample are tested and a statistical
analysis for mean, standard deviation, and coefficient of variation
percent are calculated. As reported in the examples herein and as
used throughout the claims, the Advancing Contact Angle value
represents the advancing contact angle of distilled water on a
fiber sample determined according to the preceding test method.
Similarly, as reported in the examples herein and as used
throughout the claims, the Receding Contact Angle value represents
the receding contact angle of distilled water on a fiber sample
determined according to the preceding test method.
EXAMPLES
Example 1
Fibers were prepared using varying amounts of a poly(lactic acid),
a polypropylene, and a compatibilizer. The poly(lactic acid)
polymer (PLA) was obtained from Chronopol Inc., Golden, Colo., and
had an L:D ratio of 100 to 0, a melting temperature of about
175.degree. C., a weight average molecular weight of about 181,000,
a number average molecular weight of about 115,000, a
polydispersity index of about 1.57, and a residual lactic acid
monomer value of about 2.3 weight percent. The polypropylene
polymer (PP) was obtained from Himont Incorporated under the
designation PF305 polypropylene polymer, which had a specific
gravity of between about 0.88 to about 0.92 and a melting
temperature of about 160.degree. C. The compatibilizer was obtained
from Petrolite Corporation of Tulsa, Okla., under the designation
UNITHOX.RTM.480 ethoxylated alcohol, which had a melting
temperature of about 160.degree. C. and a number average molecular
weight of about 2250.
To prepare a specific thermoplastic composition, the various
components were first dry mixed and then melt blended in a
counter-rotating twin screw to provide vigorous mixing of the
components. The melt mixing involves partial or complete melting of
the components combined with the shearing effect of rotating mixing
screws. Such conditions are conducive to optimal blending and even
dispersion of the components of the thermoplastic composition. Twin
screw extruders such as a Haake Rheocord 90, available from Haake
GmbH of Karlsautte, Germany, or a Brabender twin screw mixer (cat
no 05-96-000) available from Brabender Instruments of South
Hackensack, N.J., or other comparable twin screw extruders, are
well suited to this task. The melted composition is cooled
following extrusion from the melt mixer on either a liquid cooled
roll or surface and/or by forced air passed over the extrudate. The
cooled composition is then subsequently pelletized for conversion
to fibers.
Converting these resins into fiber and nonwoven was conducted on a
in-house 0.75 inch diameter extruder with a 24:1 L:D
(length:diameter) ratio screw and three heating zones which feed
into a transfer pipe from the extruder to the spin pack, which
constitutes the 4th heating zone and contains a 0.62 inch (about
1.6 cm) diameter Koch.RTM. SMX type static mixer unit, available
from Koch Engineering Company Inc. of New York, N.Y., and then into
the spinning head (5th heating zone) and through a spin plate which
is simply a plate with numerous small holes through which the
molten polymer will be extruded through. The spin plate used herein
had 15 to 30 holes, where each hole has a diameter of about 500
micrometers. The temperature of each heating zone is indicated
sequentially under the extrusion temperatures heading in Table 2.
The fibers are air quenched using air at a temperature range of
13.degree. C. to 22.degree. C., and drawn down by a mechanical draw
roll and passed on to either a winder unit for collection, or to a
fiber drawing unit for spunbond formation and bonding, or through
accessory equipment for heat setting or other treatment before
collection.
The fibers were evaluated for contact angle and heat shrinkage. The
composition of the various fibers and the results of the
evaluations are shown in Table 1.
TABLE 1
__________________________________________________________________________
Composition of Fiber (Wt %) Contact Angle Heat Sample # PLA PP
Compatibilizer Advancing Receding Shrinkage
__________________________________________________________________________
*1 100% -- -- 85.3.degree. 40.7.degree. 34% *2 -- 100% --
128.1.degree. 93.9.degree. 0% *3 -- 95% 5% 120.6.degree. 79.degree.
-- *4 -- 95% 5% 124.0.degree. 58.5.degree. 0% *5 95% -- 5%
89.2.degree. 10.0.degree. -- *6 70% 30% -- 92.3.degree.
56.5.degree. 0% 7 55% 37% 8% 111.7.degree. 51.4.degree. 0% 8 64%
27% 9% 117.4.degree. 40.1.degree. 0% 9 48% 39% 13% 106.3.degree.
0.degree. 0% 10 52% 35% 13% 97.6.degree. 16.8.degree. 0% 11 61% 26%
13% 88.6.degree. 5.8.degree. 0% 12 70% 17% 13% 86.7.degree.
0.degree. 0% 13 51% 34% 15% 92.8.degree. 3.3.degree. 0% 14 76.5%
8.5% 15% 86.1.degree. 0.degree. 0%
__________________________________________________________________________
*Not an example of the present invention.
Example 2
Fibers were prepared using varying amounts of a polybutylene
succinate, a polypropylene, and a compatibilizer. The polybutylene
succinate (PBS) was obtained from Showa Highpolymer Co., Ltd.,
Tokyo, Japan, under the designation Bionolle 1020 polybutylene
succinate, and had a melting temperature of about 95.degree. C., a
weight average molecular weight of between about 40,000 to about
1,000,000, a number average molecular weight of between about
20,000 to about 300,000, and a polydispersity index of between
about 2 to about 3.3. The polypropylene polymer (PP) was obtained
from Himont Incorporated under the designation PF305 polypropylene
polymer, which had a specific gravity of between about 0.88 to
about 0.92 and a melting temperature of about 160.degree. C. The
compatibilizer was obtained from Petrolite Corporation of Tulsa,
Okla., under the designation UNITHOX.RTM.480 ethoxylated alcohol,
which had a melting temperature of about 160.degree. C. and a
number average molecular weight of about 2250.
Fibers were prepared using a method essentially similar to the
method described in Example 1.
The fibers were e valuated for contact angle and heat shrinkage.
The composition of the various fibers and the results of the
evaluations are shown in Table 2.
TABLE 2
__________________________________________________________________________
Composition of Fiber (Wt %) Contact Angle Heat Sample # PBS PP
Compatibilizer Advancing Receding Shrinkage
__________________________________________________________________________
*15 100% -- -- 76.degree. 0.degree. 0% 16 61% 26% 13% 21.8.degree.
0.degree. 0% 17 70% 17% 13% 24.1.degree. 0.degree. 0%
__________________________________________________________________________
*Not an example of the present invention.
Example 3
Fibers were prepared using varying amounts of a poly(lactic acid),
a polyethylene, and a compatibilizer. The poly(lactic acid) polymer
(PLA) was obtained from Chronopol Inc., Golden, Colo., and had an
L:D ratio of 100 to 0, a melting temperature of about 175.degree.
C., a weight average molecular weight of about 181,000, a number
average molecular weight of about 115,000, a polydispersity index
of about 1.57, and a residual lactic acid monomer value of about
2.3 weight percent. The polyethylene polymer (PE) was obtained from
The Dow Chemical Company, Midland, Mich., under the designation
ASPUN.RTM. PE6811A polyethylene polymer and had a melting
temperature of about 130.degree. C. The compatibilizer was obtained
from Petrolite Corporation of Tulsa, Okla., under the designation
UNITHOX.RTM.480 ethoxylated alcohol, which had a melting
temperature of about 160.degree. C. and a number average molecular
weight of about 2250.
Fibers were prepared using a method essentially similar to the
method described in Example 1.
The fibers were evaluated for contact angle and heat shrinkage. The
composition of the various fibers and the results of the
evaluations are shown in Table 3.
TABLE 3
__________________________________________________________________________
Composition of Fiber (Wt %) Contact Angle Heat Sample # PLA PE
Compatibilizer Advancing Receding Shrinkage
__________________________________________________________________________
18 52% 35% 13% 78.3.degree. 0.degree. 2% 19 78% 9% 13% 66.3.degree.
0.degree. 9%
__________________________________________________________________________
*Not an example of the present invention.
Those skilled in the art will recognize that the present invention
is capable of many modifications and variations without departing
from the scope thereof. Accordingly, the detailed description and
examples set forth above are meant to be illustrative only and are
not intended to limit, in any manner, the scope of the invention as
set forth in the appended claims.
* * * * *